As cyan dye forming couplers in subtractive color photography, phenol couplers and naphthol couplers have been in conventional use for same time.
Recently, various cyan couplers having novel core structures have been proposed. As couplers similar to those used in the present invention, for example, JP-A 64-46752 (corresponding to U.S. Pat. No. 4,950,585; the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses 5-membered ring-6-membered ring condensed couplers in which a pyrazole ring is condensed with a nitrogen-containing 6-membered ring to form a hetero ring structure; JP-A-64-46753 (U.S. Pat. No. 4,950,585) discloses pyrazolopyrimidone couplers; JP-A-2-236545 discloses 5-membered ring-6-membered ring condensed couplers in which a pyrimidone or pyrimidinethione ring is condensed to form a nitrogen-containing 6-membered hetero ring structure, such as imidazopyrimidone, imidazopyrimidinethione and pyrazolopyrimidone couplers; and JP-A-2-190850, JP-A-2-232653 (U.S. Pat. No. 4,970,142) and JP-A-2-214857 (U.S. Pat. No. 4,970,142) disclose pyrazolo-unsym-triazin-7-one, pyrazolo-sym-triazin-5-one and pyrazolo-sym-triazin-7-one couplers, respectively.
The Japanese patent applications cited in the preceding paragraph state that these novel cyan couplers all form color images free from change of the color hue due to heat, moisture and light and that these couplers are all superior to conventional phenol and naphthol couplers described above with respect to heat resistance, moisture resistance and light resistance.
However, it has been found that, although these couplers have improved heat resistance, moisture resistance and light resistance, their coupling reactivity with an oxidation product of an aromatic primary amine developing agent is extremely low so that the amount of the coupler and the amount of silver halide emulsion to be coated must be significantly increased to obtain the necessary cyan color density. In order to overcome this problem, it has been considered important to improve the coloring capacity of the couplers in question.
Examples of conventional phenol couplers include 2-acylamino-5-alkylphenol, 2,5-diacylaminophenol and 2-ureido-5-acylaminophenol couplers, and examples of conventional naphthol couplers include 2-carbamoyl-1-naphthol and 2-carbamoyl-5-amido-1-naphthol couplers. Specific examples of conventional phenol and naphthol couplers are described in, for example, U.S. Pat. Nos. 2,369,929, 2,801,171, 2,895,826, 3,772,002, 4,052,212, 4,146,396, 4,228,233, 4,296,200, 2,772,162, 3,758,308, and 4,334,011, German Patent Laid-Open No. 3,329,729 (U.S. Pat. No. 4,463,086), European Patent Laid-Open No. 121,365 (U.S. Pat. No. 4,500,635), U.S. Pat. Nos. 4,327,173, 3,446,622, 4,333,999, 4,427,767, 4,451,559, and 4,775,616, European Patent Laid-Open Nos. 271,323, 271,324 (U.S. Pat. No. 4,775,616) and 271,325 (U.S. Pat. No. 4,753,871), U.S. Pat. Nos. 4,690,889, 4,254,212, and 4,296,199, and JP-A-61-42658 (U.S. Pat. No. 4,910,128).
However, these phenol and naphthol couplers do not satisfy all the necessary fundamental properties of couplers, including, for example, coupling reactivity of the couplers with an oxidation product of an aromatic primary amine color developing agent; properties of the color dyes to be formed from the couplers, such as the molecular extinction coefficient, the spectral absorption maximum wavelength, the green light in the short wavelength side, the absorption density in the blue light range, and the change of the color hue due to the color density; fastness of the color dyes to heat, moisture and light; resistance of the color dyes to change to leuco dyes; and stability of the color dyes with respect to change of hue with the lapse of time. The phenol and naphthol couplers in question have some drawbacks in that they do not satisfy all of the necessary properties and further improvement of them is being researched.
As mentioned above, 5-membered ring-6-membered ring condensed cyan couplers in which a pyrazole ring or imidazole ring is condensed with a nitrogen-containing 6-membered ring to form a hetero ring structure have a low coupling reactivity with an oxidation product of an aromatic primary amine color developing agent so that it is not practical to use them in silver halide color photographic materials.